Decontaminating Swift UVOT Grism Observations of Transient Sources

TL;DR

This paper introduces a new empirical method for decontaminating Swift UVOT grism spectra of transient sources, improving flux and wavelength calibration accuracy and removing spurious emission lines.

Contribution

The paper presents a novel decontamination technique for UVOT grism spectra, including required image processing steps and software implementation for community use.

Findings

Accurate flux and wavelength calibration demonstrated with SN 2011fe

Effective removal of spurious emission lines in supernova spectra

Software implementation made available to researchers

Abstract

We present a new technique of decontaminating Swift UVOT grism spectra for transient objects. We describe the template image requirements and image processing steps necessary to successfully implement the empirical decontamination technique. We demonstrate the accuracy of the flux and wavelength calibrations for decontaminated spectra by comparing a spectrum of SN 2011fe with a well-calibrated, long-slit ultraviolet spectrum from the Hubble Space Telescope's Space Telescope Imaging Spectrograph. We also show how the decontamination removes spurious emission lines from spectra of iPTF14bdn which otherwise could be misinterpreted as coming from the supernova. The software which implements this technique is briefly discussed and is made available to the community.